Smallpox

In 1988, there were approximately 350,000 cases of polio and the disease was endemic in 125 countries. Today, wild poliovirus is endemic in only three countries,1 and there were just 118 cases of polio in 2017.1,2

Rubella was eliminated from the Americas in 2015. As a result, the number of children born with birth defects caused by rubella infections – which in the 1960s amounted to tens of thousands – has fallen dramatically.4

Introduction of the Hib vaccine in 2002 has virtually eliminated Hib meningitis in Uganda. In Kilifi, Kenya, the vaccine has reduced the number of new cases of invasive Hib disease by more than 90% over a 12-year period.6

In Mexico, phased introduction of rotavirus vaccine during 2006 and 2007 led to a sustained 53% reduction in diarrhoea mortality.8 Rotavirus vaccine has also had a marked impact in Zambia, where diarrhoeal deaths among hospitalised children have declined by more than 25% since its widespread introduction.9

HOW VACCINES WORK

Vaccines help prepare the body to fight off disease-causing germs, such as bacteria and viruses. They are like training courses for the immune system – teaching it to recognise and destroy the invaders before they can do significant harm to the body.

This is how it works:

A weakened or killed form of the germ – called an antigen – is introduced into the body.

The body produces specific antibodies to fight the introduced germs. The body also produces T cells, or memory cells, which remember how to fight that specific germ.

If actual disease germs ever attack the body, the immune system is already primed and the right antibodies can return quickly to destroy them.

All vaccines used for routine immunisation are safe, rigorously tested and effective in preventing disease.

HOW VACCINES ARE DEVELOPED, TESTED AND PREQUALIFIED

Development

Vaccine development starts with the modification, killing or breaking apart of the germs that cause disease. This produces the key ingredient of all vaccines: the vaccine antigen. Several other substances – adjuvants, stabilisers and preservatives – are then added to make the new vaccines as effective and safe as possible.

Adjuvants increase the immune response to the antigen, stabilisers increase the vaccine’s storage life, while preservatives prevent contamination of vaccines by funghi or bacteria.

Vaccine development starts with the modification, killing or breaking apart of the germs that cause disease. This produces the key ingredient of all vaccines: the vaccine antigen. Several other substances – adjuvants, stabilisers and preservatives – are then added to make the new vaccines as effective and safe as possible.

Adjuvants increase the immune response to the antigen, stabilisers increase the vaccine’s storage life, while preservatives prevent contamination of vaccines by funghi or bacteria.

Testing

All new vaccines go through a series of tests and trials to make sure they are effective and safe to use. Researchers carry out vaccine trials in large groups of people, not only to be confident that a given vaccine provides a high level of protection but also to be able to detect even rare side effects.

All new vaccines go through a series of tests and trials to make sure they are effective and safe to use. Researchers carry out vaccine trials in large groups of people, not only to be confident that a given vaccine provides a high level of protection but also to be able to detect even rare side effects.

Prequalification

New vaccines can only be made available to the public after they have been successfully tested and approved for use by a country’s national regulatory authority. In addition, WHO operates a prequalification procedure which ensures that all vaccines purchased by UN agencies and international organisations, such as UNICEF and Gavi, are safe and effective and meet required quality standards.

New vaccines can only be made available to the public after they have been successfully tested and approved for use by a country’s national regulatory authority. In addition, WHO operates a prequalification procedure which ensures that all vaccines purchased by UN agencies and international organisations, such as UNICEF and Gavi, are safe and effective and meet required quality standards.

HOW IMMUNISATION DECISIONS ARE MADE

At the global level

WHO is required to provide member states with evidence-based recommendations on vaccines and immunisation. In 1999, WHO established an independent advisory group, the Strategic Advisory Group of Experts (SAGE) on Immunization, to fulfil its mandate. SAGE provides guidance to WHO on global immunisation policy and strategies. Its remit is not confined to childhood diseases and vaccines but extends to all vaccine-preventable diseases and immunisation programmes.

At the country level

National immunisation technical advisory groups (NITAGs) provide independent, evidence-informed expert advice to national policy makers and immunisation programme managers on policy issues related to immunisation and vaccines. Ministries of health, in conjunction with other parts of national governments such as ministries of finance, ultimately make the decisions about which vaccines should be provided through national immunisation programmes.

HOW VACCINE SAFETY IS MONITORED AND REGULATED

Very few public health interventions have been as successful as immunisation in improving health and saving lives. Hundreds of millions of doses of vaccine are safely administered every year.

A small minority of children and adults experience adverse side effects as a result of their vaccinations. The vast majority of side effects are minor, but in rare cases individuals can have a mild or serious reaction to a vaccine. Even then, most reported events turn out not to be due to the vaccine itself. Many are simply coincidental events, while others (particularly in developing countries) are due to human or programme error in how the vaccine is administered or stored.

The surveillance of adverse events following immunisation is a critical monitoring function of national regulatory authorities and national immunisation programmes . It means that abnormalities in the vaccine or programme, should they occur, will be quickly picked up and appropriate action taken. This is especially important when many doses are administered in a very short time, for example during vaccination campaigns.